The present invention relates to a distributed accumulator for attenuating pressure oscillations in oil channels of a hydraulic valve actuation system.
Internal combustion engines typically include intake and exhaust valves which are operated by cams on a camshaft associated with the engine. Camless engines with electrically or hydraulically controlled valves have been proposed to provide improved control of valve operation in order to achieve valve movement which does not depend upon the contours of a cam surface. For example, an electrically or hydraulically controlled engine may enable valves to open multiple times during an engine cycle, or not at all, such as in a cylinder deactivation system. Electrically or hydraulically controlled valves may make timing adjustment easier and provide fully flexible valve actuation control.
In a hydraulically controlled valvetrain, variations in hydraulic pressure within the oil supply, oil return and control passages may alter the performance of the valve train. If the pressure oscillations are too high in amplitude and/or not of consistent phase in relation to each valve event, valve position control may be lost. This may result in erratic valve train dynamics, valve train noise, and potential valve-to-piston interference or engine failure. Accordingly, it is desirable to attenuate such pressure oscillations.
The present invention provides a distributed accumulator for use in the oil supply, oil return, and/or control channels of a manifold for a hydraulic camless valve actuation system. The distributed accumulator is configured to attenuate pressure oscillations in the oil resulting from oil flow oscillations during actuation of switching valves.
More specifically, a manifold is provided for distributing high pressure oil on a camless engine. The manifold includes a body having first, second and third channels formed therein lengthwise in the body. Switching valves on the body are operative to alternately communicate oil in the channels with cylinder valves (via force translators) of an engine to which the manifold is mounted to affect movement of the cylinder valves. A distributed accumulator is positioned in one of the channels and includes at least one compliant pocket filled with a compressible fluid. The accumulator is configured such that the pocket attenuates pressure oscillations in the oil resulting from oil flow oscillations during actuation of the switching valves.
Preferably, the distributed accumulator is positioned in an oil return channel (the first channel), and a second distributed accumulator is positioned in the control channel (the second channel).
A plurality of compliant pockets may be spaced along the length of each distributed accumulator, or a single compliant pocket may extend substantially the length of each distributed accumulator.
Each distributed accumulator may also have a holder portion formed at an end thereof and having a contour matching the contour of the respective channel to secure the distributed accumulator within the respective channel.
Preferably, each pocket has a stainless steel membrane with a compressible fluid trapped therein. The compressible fluid may be an inert gas such as nitrogen or air, for example.
The invention also contemplates a camless engine including intake and exhaust valves controlled by oil pressure within manifolds as described above. The switching valves selectably communicate the high pressure or low pressure oil with the cylinder valve through a fluid aperture (via a force translator, for example) to affect movement of the cylinder valve between open and closed positions. In order to attenuate pressure oscillations and provide smooth valve closure, a distributed accumulator is positioned in at least one of the oil supply, oil return, and control channels of the manifold.